OSI Network Model in FE Electrical

Understanding network models in FE Electrical is key to understanding the networking principles and data transmission architecture. This important FE Electrical exam topic, according to the NCEES® exam roadmap, also connects with other core topics of data and networking.

This detailed study guide will help you discover all the ins and outs of the OSI model in FE Electrical. Let’s unfold this vital architecture of network models in FE Electrical in detail.

OSI Model

The OSI (Open Systems Interconnection) Model is a conceptual framework used to understand and standardize the functions of a telecommunication or computing system without regard to its underlying internal structure and technology.

The model partitions the data flow in a network into seven abstract layers, each with unique functionalities and standards.

Why the OSI Model is Effective?

Modularity: It breaks down the network communication process into smaller and simpler components, improving flexibility and manageability.

  • Standardization: Facilitates interoperability between different products and software.
  • Troubleshooting: Easier to identify and address network issues in a layered approach.
  • Adaptability: Can adapt to new technologies and protocols.

Layers of OSI Model

Layers of OSI Model

There are 7 OSI model layers.

  1. Physical Layer
  2. Data Link Layer
  3. Network Layer
  4. Transport Layer
  5. Session Layer
  6. Presentation Layer
  7. Application Layer

Each OSI model layer interacts directly only with the layer immediately above and below it, creating a layer of abstraction. Data encapsulation and decapsulation happen as data moves through the layers.

  • Encapsulation: As data descends through the layers, each layer adds its header (and sometimes a trailer) to the data unit from the layer above. For example, the Network layer adds IP headers to the data, which the Data Link layer then frames.
  • Decapsulation: As data ascends, each layer removes its corresponding header (and trailer) to hand over the pure data to the next layer.

This process ensures that each layer remains independent and changes in one layer do not directly affect the others. Let’s unwrap what happens at each layer of the OSI Model.

1. Physical Layer

Components and Transmission: This layer is concerned with the physical connection between devices, including aspects like voltage levels, data rate, maximum transmission distance, and physical connectors. It deals with the hardware elements like cables (coaxial, fiber optic), hubs, and repeaters.

Data Conversion and Security: Data is transmitted as raw bits over a physical medium. The physical layer provides the means of transmitting these bits but offers no security measures.

2. Data Link Layer

Components and Transmission: This layer provides node-to-node data transfer—a link between two directly connected nodes. It detects and possibly corrects errors that may occur in the physical layer. Components include switches, bridges, and network interface cards (NICs). It uses MAC addresses for addressing and is divided into two sublayers: Logical Link Control (LLC) and Media Access Control (MAC).

Data Conversion and Security: Frames are the data units at this layer. It encapsulates network layer packets into frames, adding a header and a trailer to each frame. For security, it can implement MAC address filtering and some forms of encryption.

3. Network Layer

Components and Transmission: This layer handles packet forwarding, including routing through intermediate routers. It’s where you’ll find routers, layer three switches, and protocols like IP (Internet Protocol). It uses IP addresses for addressing.

Data Conversion and Security: Data units are packets at this layer. It adds source and destination IP address information to each packet. Security measures include firewalls and IPsec for encrypting internet protocol communications.

4. Transport Layer

Components and Transmission: The transport layer provides end-to-end application communication services. It establishes, manages, and terminates connections between hosts. It uses protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

Data Conversion and Security: The data units are segments (TCP) or datagrams (UDP). This layer is responsible for error recovery and flow control. Security is enhanced here with SSL/TLS encryption protocols.

5. Session Layer

Components and Transmission: This layer controls the dialogues (connections) between computers. It establishes, manages, and terminates connections between local and remote applications. It’s used less in modern networks but is important in applications like remote procedure calls.

Data Conversion and Security: The session layer does not involve lower-level data formatting, focusing on establishing and maintaining connections. Security is more about managing sessions securely.

6. Presentation Layer

Components and Transmission: This layer translates data between the application and network layers. It’s also involved in data encryption and compression. It ensures that data is in a usable format and can be understood by the application layer.

Data Conversion and Security: It converts data from a format used by the application layer into a common format at the sending station, then back into a format understandable to the application layer at the receiving station. Encryption and decryption are key security functions at this layer.

7. Application Layer

Components and Transmission: This layer supports application and end-user processes. It provides a way for applications to access network services. Examples of application layer functionalities include HTTP for web browsing, SMTP for email, and FTP for file transfer.

Data Conversion and Security: This layer doesn’t alter data format but instead focuses on providing protocols that applications use to exchange data. Security measures include various application-level protocols like HTTPS for secure web browsing.

Now, you can understand how each layer in the OSI model only communicates with its direct upper and lower layers. The data unit is passed down the layers on the sending side, each adding its own header information.

It is then passed up to the layers on the receiving side, where the headers added by the corresponding sending layers are removed. This ensures structured and modular communication, although not all layers are always used in every communication model, and the OSI model itself is more a guideline than a strict rulebook in modern network design and operation.

The Flow of Data Packet in the OSI Model – Step-by-Step Process

The data flow in the OSI model is a complex process involving various layers, each with specific functions and protocols. Let’s examine the flow of a packet from top to bottom (application to physical) and bottom to top (physical to application), along with scenarios where a packet might be stopped at each layer and the resulting security implications.

Top to Bottom (Application to Physical Layer)

Application to Physical Layer
1. Application Layer

Flow: The process begins with data generation at the application layer. This data could be a file, email, or webpage request.

Stopped: The application layer might stop a request if it is malformed or unauthorized. Security software might also block suspicious outbound requests, protecting against data leaks or malware communication.

2. Presentation Layer

Flow: Data is formatted, encrypted, or compressed if necessary.

Stopped: If encryption fails or data cannot be properly formatted, it’s halted. This prevents the transmission of potentially unreadable or unsafe data.

3. Session Layer

Flow: Establishes a session between two end systems.

Stopped: If the session can’t be established due to authentication issues or session timeouts, transmission stops. It’s a basic security measure to ensure communication only occurs between authenticated parties.

4. Transport Layer

Flow: Establishes end-to-end communication and breaks data into smaller packets.

Stopped: Transmission is halted if there’s a failure in segmenting data or establishing a connection (e.g., due to port blocking or TCP handshake failure). This layer is crucial in preventing unauthorized access and ensuring reliable communication.

5. Network Layer

Flow: Adds IP addresses and routes the packet.

Stopped: If the destination is unreachable or the packet is routed incorrectly, it stops. Network layer security, like firewalls, can also block packets based on IP addresses, protecting against network-based attacks.

6. Data Link Layer

Flow: Frames the packet with MAC addresses and error-checking information.

Stopped: If there’s an error in addressing or a collision on the medium, the frame might not be sent. MAC address filtering can also be used to restrict network access.

7. Physical Layer

Flow: Converts frames into electrical, radio, or optical signals.

Stopped: Physical issues like broken cables, disconnected networks, or signal interference can stop the transmission. Physical layer security is about ensuring the physical integrity of the network infrastructure.

Bottom to Top (Physical to Application Layer)

physical to application layer
1. Physical Layer

Flow: Receives the signal and converts it into digital data.

Stopped: The data won’t be passed up if signals are corrupted or lost due to physical issues.

2. Data Link Layer

Flow: Processes frames and checks for errors.

Stopped: The frame is discarded if an error is detected or the MAC address doesn’t match. This prevents corrupted or misaddressed data from propagating.

3. Network Layer

Flow: Routes the packet to the correct destination based on IP addresses.

Stopped: If the packet’s destination is unreachable or a router’s security policy blocks it, it’s halted. Firewalls at this layer are crucial in filtering unwanted or harmful traffic.

4. Transport Layer

Flow: Reassembles segments into complete data and checks for errors.

Stopped: If segments are missing or corrupted or the destination port is closed, the data won’t be reassembled. This layer ensures that only complete and correct data is passed to the application layer.

5. Session Layer

Flow: Manages and maintains the communication session.

Stopped: Data transmission is halted if the session is interrupted or unauthorized. This ensures communication continuity and security.

6. Presentation Layer

Flow: Decrypts and formats data for the application layer.

Stopped: If decryption fails or the format is incorrect, the data is unusable and stopped. This layer ensures that data is in a readable and secure format for the application.

7. Application Layer

Flow: Receives and processes the data for the user or application.

Stopped: If the data is irrelevant or unrecognized by the application, it might be discarded. Application-level security measures (like firewalls and anti-virus software) can also block data deemed harmful or suspicious.

Security Outcome

The security implications of the OSI above posture at each layer are, therefore,

  • Application Layer: Focus on data validation, application security policies, and endpoint protection.
  • Presentation Layer: Ensure proper encryption/decryption and data formatting.
  • Session Layer: Manage session integrity, authentication, and reconnection policies.
  • Transport Layer: Implement secure transmission protocols (like TLS), port security, and connection monitoring.
  • Network Layer: Use firewalls, intrusion detection systems (IDS), and routing policies.
  • Data Link Layer: Apply MAC address filtering, switch security

Read the other part of this guide here to understand how the TCP/IP model works and why it’s an important network model in the FE Electrical exam.


You now have a rich idea of Network Models in FE Electrical and how the OSI model works. By understanding how different layers in the OSI model interact to ensure a seamless and secure data flow, you can tailor these architectures to protect data at each stage of its journey through the network (Source to Destination).

This layered approach simplifies and allows for in-depth defense, addressing potential vulnerabilities at multiple levels in the network stack.

For an effective FE Electrical exam preparation, we recommend you check our comprehensive study resources, guides, and preparation courses at Study for FE – your go-to place for all things FE-related.


Licensed Professional Engineer in Texas (PE), Florida (PE) and Ontario (P. Eng) with consulting experience in design, commissioning and plant engineering for clients in Energy, Mining and Infrastructure.